1. Field of the Invention
The present invention relates to a printing and thermal activation method and device for a heat-sensitive adhesive sheet having a printable layer on one side and a heat-sensitive adhesive layer on the other side.
2. Description of the Related Art
In recent years, most of commonly used sticker labels as barcode labels or price stickers are such that a heat-sensitive adhesive layer is formed on an opposite side of a recording surface (printable layer) and release paper (separator) is stuck and temporarily bonded onto the heat-sensitive adhesive layer when in storage. However, this type of sticker label is disadvantageous in that the release paper needs to be peeled off from the heat-sensitive adhesive layer before use in label form, which inevitably involves wastes.
To cope with this, there have been developed as a release-paper-free system, a heat-sensitive adhesive label having a sheet-like base material on a rear side of which a heat-sensitive adhesive layer is formed, the layer exhibiting no adhesion in normal state but exhibiting the adhesion under heat, and a thermal activation device for heating the heat-sensitive adhesive layer formed on a rear surface of the heat-sensitive adhesive label to thereby bring out its adhesion.
For example, devices employing various heating systems such as a heating roll system, a hot air blower system, an infrared radiation system, and a system using an electrothermal heater or induction coil have been proposed for the thermal activation device. For example, JP 11-079152 A ([0024] and [0025], FIGS. 1 and 2) discloses a technique for bringing a head having as a heat source plural resistors (heater elements) provided on a ceramic substrate into contact with a heat-sensitive adhesive label to heat a heat-sensitive adhesive layer like a thermal head used as a print head for a thermal printer.
Here, a typical structure of a conventional printer for a heat-sensitive adhesive sheet will be explained with reference to a thermal printer of FIG. 15.
The thermal printer of FIG. 15 is a printing and thermal activation device including: a roll housing unit 20 for holding a rolled heat-sensitive adhesive sheet 60; a printing unit 30 for printing on the heat-sensitive adhesive sheet 60; a cutter unit 40 for cutting the heat-sensitive adhesive sheet 60 into a label with a predetermined length; and a thermal activation unit 50 as a thermal activation device for thermally activating a heat-sensitive adhesive layer of the heat-sensitive adhesive sheet 60 in the form of a single cut label.
The heat-sensitive adhesive sheet 60 has a structure where a heat-insulating layer and a heat-sensitive color-developing layer (printable layer) are formed on a front side of a sheet base material and a heat-sensitive adhesive layer is formed on a rear side thereof by applying and drying a heat-sensitive adhesive, for example.
The printing unit 30 includes: a thermal print head 32 having plural heater elements 31 composed of relatively small resistors arranged in a width direction so as to enable dot printing; and a printing platen roller 33 brought into pressure contact with the thermal print head 32 (heater element 31). In FIG. 15, the printing platen roller 33 rotates clockwise, by which the heat-sensitive adhesive sheet 60 is transported from the left to the right in FIG. 15.
The cutter unit 40 is used for cutting into an appropriate length the heat-sensitive adhesive sheet 60 printed with the printing unit 30 and composed of a movable blade 41 operated by a drive source (not shown) such as an electric motor and a stationary blade 42 facing the movable blade 41, for example.
The thermal activation unit 50 includes: a thermal-activation thermal head 52 serving as heating means and provided with a heater element 51; a thermal activation platen roller 53 as transporting means for transporting the heat-sensitive adhesive sheet 60; and a draw-in roller 54 for drawing the label-like heat-sensitive adhesive sheet 60 fed from the printing unit 30 side in between the thermal-activation thermal head 52 (heater element 51) and the thermal activation platen roller 53. In FIG. 15, the thermal activation platen roller 53 rotates in a (counterclockwise) direction reverse to the rotation direction of the printing platen roller 33 to transport the label-like heat-sensitive adhesive sheet 60 in a predetermined direction (to the right).
Note that if the heat-sensitive adhesive sheet 60 irregularly sags when transported, wrinkles may develop on the sheet or any transport failure is more likely to occur. Hence, in general, a transport speed (print speed) of the printing platen roller 33 is matched with a transport speed (activation speed) of the thermal activation platen roller 53.
With the thermal printer thus structured, after the heat-sensitive adhesive sheet 60 exhibits adhesion, it is possible to label the heat-sensitive adhesive sheet as-is in the form of an indicator label, onto cardboard cartons, wrapping for foods, glass bottles, or plastic containers or in the form of a price sticker or advertisement label. Therefore, it is possible to dispense with the release paper used for conventional, typical sticker labels to realize cost reduction. Also, the label thus prepared is desirable from the viewpoint of recourse-saving and environmental protection on account of requiring no release paper that may end up in wastes after the use.
With the aforementioned conventional structure, the printing unit 30, the cutter unit 40, and the thermal activation unit 50 are arranged in line and require power sources for driving. The structure has a disadvantage that the entire device is large and cumbersome. In addition, such a structure requires transporting means for transporting the heat-sensitive adhesive sheet 60 while smoothly transferring the sheet among the printing unit 30, the cutter unit 40, and the thermal activation unit 50. Thus, a structure and control for the entire device are complicated when aiming at continuously and efficiently performing printing and thermal activation on the heat-sensitive adhesive sheet 60 while synchronizing the transport of the heat-sensitive adhesive sheet 60 with the transporting means with operations of the printing unit 30, the cutter unit 40, and the thermal activation unit 50. Further, an expensive thermal head is necessary for both the printing unit 30 and the thermal activation unit 50, leading to an increased cost of the entire device.
Also, the heat-sensitive adhesive layer of the heat-sensitive adhesive sheet 60 is thermally activated under heat in abutment with the surface of the thermal-activation thermal head 52 of the thermal activation unit 50 to exhibit adhesion. However, the heat-sensitive adhesive layer may adhere to the thermal-activation thermal head 52 due to its adhesion and slightly peel off from the base material and remain on the surface of the thermal-activation thermal head 52 as adhesive residues. As a result, a foreign matter as the adhesive residue exists between the thermal-activation thermal head 52 and the thermal activation platen roller 53, which lowers reliability of movement of the heat-sensitive adhesive sheet 60 from that point forward. There is a possibility that the smooth transport of the sheet cannot be maintained. To prevent this, it is necessary to clean the head at regular intervals.
The general heat-sensitive adhesive sheet 60 lacks in keeping the adhesion exhibited by thermal activation, and the strong adhesion can be only kept for about 1 minute. Thus, in the case of continuously performing printing and thermal activation on the heat-sensitive adhesive sheet 60 with the aforementioned conventional structure, a function of the adhesive sheet is lost unless labeling is completed in a short time. Accordingly, it is impossible to prepare a large amount of sticker labels in advance and collectively affix the labels later, i.e., so-called batch-labeling. This means that the sticker labels are produced one by one or in small amounts and successively affixed, imposing limitations on the application as the adhesive sheet.